The 135 mm F3.5 Pentax M lens is not to be sneezed at, dealer price in near-mint condition should be £40 - £50. I particularly like the Pentax 200 mm f4 M lens - I had one that was great, sold it, regretted it, and bought another that was equally great. One will probably cost £60. For about half this cost, lots of zooms by Tamron, Sigma, etc.